It is well known that aluminum alkoxide structures are very complex. A summary of these structures, properties, etc., is found in Bradley et al., Metal Alkoxides, Academic Press, New York (1978), pages 78 to 81. Moreover, the use of these aluminum alkoxides in paints and coatings is also known, e.g. as discussed in the article published by Turner et al., The Function of Aluminum Complexes as Structure Modifiers for Paint, Journal of the Oil and Color Chemists Association, Vol. 41, November 1958, pages 769 et seq.
The production of aluminum alcoholates, i.e. aluminum alkoxides and liquid aluminum alkoxides and the like, has also been disclosed in a number of U.S. patents of which the following are known to the inventor: U.S. Pat. No. 2,687,423 issued Aug. 24, 1954 to Mesirow; U.S. Pat. No. 2,845,447 issued July 29, 1958 to Carlson et al.; U.S. Pat. No. 3,006,941 issued Oct. 31, 1961 to Mudrak et al.; U.S. Pat. No. 3,068,263 issued Dec. 11, 1962 to Smith; U.S. Pat. No. 3,305,571 issued Feb. 21, 1967 to Cenker; U.S. Pat. No. 3,920,713 issued Nov. 18, 1975 to Feichtinger et al.; U.S. Pat. No. 4,052,428 issued Oct. 4, 1977 to Lerner et al.; and U.S. Pat. No. 4,132,724 to Turner.
Aluminum alkoxides having the structural formula ##STR1## are referred to as aluminum tri-alkoxides and are desirable in cases where tri-functionally (i.e. three reactive sites) is desired. The monomeric structure ##STR2## is used for ease of identification, although in actual occurrence there may be two, three, four or more of these aluminum tri-alkoxide molecules joined together by intermolecular forces to form corresponding dimeric, trimeric, tetrameric, or higher polymeric forms of the chemical. An example of the trimeric form of an aluminum tri-alkoxide as proposed in the above mentioned Bradley reference is: ##STR3## By the same reference, a proposed structure for the tetrameric form of an aluminum tri-alkoxide is: ##STR4## Whether the aluminum tri-alkoxide is in the monomeric, dimeric, trimeric, tetrameric, or higher polymeric form, it is always referred to as tri-functional because there are three reactive OR groups per atom of aluminum.
From the above literature and patent disclosures it is seen that one of the important considerations has been improved stability of the aluminum tri-alkoxides to hydrolysis and to solidification. This stability has been sought to be achieved by introducing acid groups or other reactive groups as replacements for one or more of the OR groups per atom of aluminum. In cases where stabilization is achieved by substituting an acid or other reactant group for one of the OR groups, it can be seen that the functionality of the aluminum compound is thereby reduced.
As discussed in the above mentioned literature references, these aluminum compounds react with moisture, hydroxyl groups, carboxylic acids, carboxyl groups present in other compounds, and carboxylic acid anhydrides. Hence, the usefulness of these compounds has been well established. However, an important commonly available aluminum tri-alkoxide, aluminum tri-isopropoxide, undergoes a physical change from a liquid to a solid during storage. This phenomenon has been described in the above mentioned literature and is explained herein. The polymeric structure of the aluminum isopropoxide is believed to be dimeric, trimeric, or a mixture of both when the product is first made. Upon ageing at ambient temperatures, it is generally believed to convert to the tetrameric form, which is a crystalline solid having rather poor solubility characteristics as compared to the freshly made compound in the liquid state.
Thus, aluminum tri-isopropoxide is only commercially available in the form of the solid tetramer, which is usually reduced to a finely divided powder prior to sale and use. Aluminum tri-alkoxides are highly reactive to atmospheric moisture, such reaction greatly reducing the activity of the product. The extremely high surface area of powdered aluminum tri-isopropoxide drastically increases the chance for moisture contact and thereby adversely affects the stability. Also, the solid tetrameric form has poor solubility in aliphatic solvents such as ink oils, and in many cases is only soluble at elevated temperatures.
On the other hand, aluminum tri-secondary butoxide remains liquid in storage at ambient temperatures and is often used in place of aluminum tri-isopropoxide where a tri-functional aluminum alkoxide is desired. However, aluminum tri-secondary butoxide also suffers from a number of serious shortcomings. One of these shortcomings is that the cost of secondary butyl alcohol is higher than that of isopropyl alcohol, making the cost of the aluminum tri-secondary butoxide generally higher than the cost of aluminum tri-isopropoxide. Another serious shortcoming of aluminum tri-secondary butoxide is that it typically has a flash-point lower than 100.degree. F., which property requires it to be shipped and stored as a hazardous "red label" material. Many of the ink and other manufacturing plants desiring to use an aluminum tri-alkoxide are located in areas where the use and/or storage of "red label" materials is prohibited or in areas where insurance premiums would have to be drastically increased if "red label" materials were to be introduced. This "red label" condition of aluminum secondary butoxide can be eliminated by making a very dilute solution of the compound in ink oil solvents having a high boiling point prior to shipment from the plant in which the compound is manufactured. However, this practice increases manufacturing costs and presents an unreasonable increase in freight costs to the customer.
It is obvious that the industry would be greatly benefitted by the development of an aluminum tri-alkoxide that does not suffer from the shortcomings of the prior art. It is the object of this invention to disclose novel aluminum tri-alkoxide compounds which are composed mostly of isopropyl moieties and yet have improved properties with respect to resistance to solidification, increased solubility in hydrocarbon solvents, and also have improved flash point properties.